Ridged waveguide magic tee



April 1967 H. L. BUNN ETAL RIDGED WAVEGUIDE MAGIC TEE Filed March 8, 1965 F/GZ INVENTORS HARLIN L. BUNN CLIFTON L. WHITTEN A TTORNEY F/GZ United States Patent Ofifice 3,315,183 Patented. Apr. 18, 1967 3,315,183 RIDGED WAVEGUIDE MAGIC TEE Harlin L. Bunn, Princeton, NJ, and Clifton L. Whitten,

Livermore, Califi, assignors to The Regents of the University of California, Berkeley, Calif.

Filed Mar. 8, 1965, Ser. No. 437,814 6 Claims. c1. 333-11) The present invention relates to waveguide junctions and more particularly to magic tee waveguide junctions. Conventional magic tee Waveguide junctions, which constitute the so-called matched hybrid-T junctions, comprise four rectangular waveguides each having a characteristic impedance Z In a magic tee-type junction, the four waveguides intersect each other in such a manner that two of the guides are collinear, constituting the main waveguide, and the other two guides or arms are at right angles from each other and from the collinear arms. One of the non-collinear arms, identified as the E-arm because it is connected to the main waveguide in the E plane, is coupled to the main waveguide in a series circuit. The other non-collinear arm, identified as the H- arm because it is coupled to the main waveguide in the H plane is coupled to the non-collinear arms in a parallel circuit. The termination of the E-arm at the junction is thus equal to 2Z (where Z is the characteristic impedance of the waveguide) while the termination of the -arm is 2 /2.

Magic tee waveguide junctions possess many of the qualities of a bridge. For example, if the collinear arms have the same length and are identically terminated at the point of juncture in the magic tee, power delivered to the system at the H-arm would divide equally between the collinear arms and no output would be present at the E-arm. Similarly, if power were delivered to the system at the E-arm, no output would be present at the -arm and the power would divide equally in the two collinear arms.

On the other hand, if power is delivered to the system at the H-arm and the terminations of the collinear arms at the point of juncture are not identical, an Output will be present at the E-arm. The output signal at the E-arm will then be proportional to the difference between the waves reflected at the collinear arms.

Thus, the junction mismatch described above causes cross-coupling between the E-arm and the H-arm, although as described above, ideally power delivered into either one of the E- or H-arms would divide equally into the main waveguide lines with no power transfer into the other one of the H- or E-arms respectively.

In order to avoid such crosstalk between the noncollinear arms, i.e., to prevent reflections that set up standing waves in the non-collinear arms, the usual practice has been to provide reactive elements such as posts, rods or irises in the waveguides. Ordinarily, such reactive elements effectively reduce such standing waves at the frequency for which they have been designed but the effective frequency range of operation is too narrow for many applications.

In addition, some waveguide junctions disclosed in the prior art utilize reactive matching structures having reactances which are more or less distributed, and which provide improved performance over the substantially lumped reactances presented by irises, rods, and like type reactive elements. Such somewhat distributed reactance type discontinuities, however, only provide matching over approximately 40% of the waveguides usable range, for the type mode operation normally employed.

Accordingly, it is an object of this invention to provide an improved magic tee waveguide-junction having substantially the full waveguides usable frequency range.

It is another object of this invention to provide a magic 2 tee waveguidejunction comprising ridged portions in the waveguide arms, selectively tapered and extending longi' tudinally through the length of the arms up to the point of juncture, to provide the desired impedance matching at the juncture point and hence wide frequency range characteristics.

A waveguide-junction embodying the invention comprises four recatangular waveguides of equal cross-section joined to each other in the so-called magic tee configuration. Two of the waveguides or arms constitute the main waveguide, and are joined to each other in endto end relationship forming collinear arms. The other two arms are respectively joined to each other and to the main waveguide at right angles. These non-collinear arms are located in the E and H planes respectively, and are therefore identified as the E and H arms. Each of the waveguides forming the collinear arms comprise an internal central ridge integrally formed on one of the rectangular broad sidewalls and extending along the longitudinal axis of the waveguide. The central ridge of each collinear arm is tapered down to a predetermined width at the point of juncture of the four waveguides. One of the non-collinear arms, the H-arm, includes a central integrally formed ridge similar to the ridges of the collinear arms, except that the cross-section of the ridge in the H- arm expands to a predetermined area from the free end of the waveguide towards the point of juncture. The other non-collinear arm, the E-arm, comprises a conventional double ridged waveguide having uniform crosssectional area and ridges running along opposite broad sidewalls of the waveguide.

The novel features of the invention are set forth in greater degree of particularity in the following detailed specification and claims, and it will be better understood when read in connection with the accompanying drawings in which:

FIG. 1 is a perspective view of a hybrid T junction, partially broken to show the point of juncture of the four arms;

FIG. 2 is a sectional elevational view in the plane defined by section lines 2-2; and

FIG. 3 is a plan sectional view of the: device of FIG. 1, taken in a plane immediately above the top walls of the collinear and parallel arms of the junction.

Referring to the drawings the illustrated hybrid-T Waveguide-junction 10 comprises a pair of collinear arms 1-2 and 12a joined to each other in end-to-end relationship to form the main waveguide. Each of the pair of collinear arms has a rectangular cross-section. Solid ridges 14 and 14a are centrally located on one of the broad rectangular sidewalls of arms '12 and 12a respectively, and extend along the longitudinal axis of the corresponding collinear arm. Each of the ridges 14 and 14a tapers, as illustrated in FIGS. 1 and 2 and as will be described later on, from a given cross'section at the free end of the guide to a smaller rectangular crosssection at the point of juncture with the other arms.

As is well known in the waveguide art, waveguides are hollow conducting tubes used to transmit electromagnetic waves. The most frequently used type of waveguide has a rectangular cross-section, as illustrated in FIG. 1 for example. In such a guide, the preferred mode (field configuration) of operation is the so-called dominant mode in which the cutoff wavelength has the greatest value. In the dominant mode the electric field is transverse to the guide axis, and extends between the two walls that are closest together, i.e., between the top and bottom walls. Each of the arms forming the magic tee waveguide-junction embodying the invention has a rectangular cross-section whose transverse dimensions are in the ratio two-to-one approximately, i.e., the width is approximately twice as large as the height.

The magnetic field, in turn, is in the form of loops which lie in planes that are at right angles to the electric field, i.e., planes parallel to the top and bottom of the guide. The magnetic field arrangement is the same in all of these planes, irrespective of the position of the plane along an axis parallel to the side walls.

An arm 16, lying in the E plane, is coupled to the collinear arms 12 and 12a, forming the main waveguide, at a right angle therefrom on the broad sidewalls of arms 12 and \12a opposite the ridges 14 and 14a. The arm 16 includes a pair of rectangular ridges 18 and 20 located on opposite narrow sidewalls of the arm 16. The rid es 18 and 20 have uniform cross-section throughout their entire length, and such ridges extend along the longitudinal axis of the arm v16 from the free end of arm 16 to the waveguide-junction point of juncture.

Ridged waveguides, well known in the waveguide art, provide the advantage of increasing the cutoff wavelength and of widening the frequency range over which only the dominant mode will propagate. As previously mentioned, however, because the attenuation per unit length provided by ridged structures is greater than the attenuation provided by corresponding rectangular guides, the use of ridged structures has been limited to special applications such as means for coupling a coaxial line to a waveguide, for example.

An arm 22 which lies in the H plane, is also coupled to the main waveguide at a right angle therefrom at one of the narrow sidewalls and also at a right angle from the double-ridged arm 16. The arm 22 includes a centrally located ridge 24 integrally formed and extending along the longitudinal axis of the bottom wall of the arm 22 on the broad sidewall furthest from the arm 16. The ridge 24 is also of rectangular cross-section. The crosssection of ridge 24, however, tapers from a given crosssectional area at the free end of the guide to a predetermined expanded restangular cross-sectional area at the point of juncture. The ridge 24 is coupled adjacent its top surface to the ridges 14 and 14a of the main waveguide adjacent their top surfaces by a coupling plate 23.

Transitional coupling means, not shown, are coupled to the magic tee waveguide junction to connect the ridged Waveguides to conventional rectangular waveguides, and hence to transmit the energy to a desired load or any desired utilization means.

As previously pointed out, the various tapered ridges and the doubly ridged arm effect an impedance match of all the arms at the point of juncture. The characteristic impedance Z,, of a ridged waveguide is a function of the width of the ridge. Thus, the value of the impedance may be increased by decreasing the width of the ridge, or the impedance may be decreased by increasing the width of the ridge.

In a conventional magic tee junction, the arm 22, which is ordinarily known as the H-arm, and which has a characteristic impedance Z is coupled to the waveguide in parallel, and terminated in the impedance Z /Z at the point of juncture. By properly decreasing the width of the main waveguide ridge, the parallel impedance presented to the H-arm 22 is increased and hence matching with the impedance exhibited by the arm 22 is thereby effected.

In turn, the arm 16 utilizes a double ridge to match the terminating impedance at the junction, which because of the tapered ridges in the main waveguide exhibits a value of impedance greater than twice the value 9f the characteristic impedance of the waveguide,

Avoltage standing wave ratio (VSWR) of less than 1.5 in both arms 16 and 22 has been obtained over a frequency range between 13 and 40 kmc. when matching of the different arms of the junction was effected in the manner previously described.

What is claimed is:

1. A waveguide junction comprising in combination: a plurality of rectangular hollow waveguides connected to each other in a magic tee configuration, each of said waveguides having at least one solid ridge formed on a side thereof, a plurality of said ridges being tapered from a first cross-sectional area at the free end of the corresponding waveguide to a second cross-sectional area at the point of juncture to provide impedance matching the junction over a wide frequency band.

2. A magic tee waveguide-junction as defined in claim 1, and wherein one of said rectangular hollow waveguides includes a pair of solid ridges of uniform crosssectional area.

'3. A magic tee waveguide-junction as defined in claim 1 wherein one of said plurality of ridges tapers from a given cross-sectional area at the free end of the corresponding waveguide to a relatively larger cross-sectional area at the point of juncture of said weveguide and wherein two of the other remaining waveguides include ridges that taper to a relatively smaller cross-sectional area at the point of juncture of said waveguide.

4-. A waveguide magic tee junction comprising four rectangular hollow waveguides joined at a common junction to form two collinear arms, a series arm perpendicular to said collinear arms on the top thereof and a parallel arm perpendicular to said collinear arms and to said series arm, each of said collinear arms having a rectangular cross-section ridge integrally formed on the bottom wall extending along the entire length thereof, and tapered from a given cross-sectional area at the free end of the corresponding collinear arm to a relatively smaller cross-sectional area at the point of juncture of the arms, said series arm having integrally formed ridges of uniform cross-section on opposite side Walls of the series arm to match the impedance presented by said junction; said parallel arm including a centrally formed integral ridge extending on the bottom wall of the parallel arm along the longitudinal axis thereof, tapered from a given cross-sectional area at the free end of the parallel arm to a relatively larger cross-sectional area at said point of juncture to match the impedance presented by the junction.

5. A waveguide magic tee junction as defined in claim 4, wherein said series arm matches the impedance presented by said junction and which is larger than twice the characteristic impedance of said waveguide, and wherein said parallel arm matches an impedance which is larger than one half of the characteristic impedance of said waveguide.

'6. A waveguide magic tee junction as defined in claim 4, wherein said arms are of equal cross-sectional area each comprising two pairs of opposite narrow and broad walls respectively, and wherein the ridges of said series arm are respectively located on said narrow walls of said arm.

No references cited.

HERMAN KARL SAALBACH, Primary Examiner,

NUSSBAUM, Assistant Examiner, 

1. A WAVEGUIDE JUNCTION COMPRISING IN COMBINATION: A PLURALITY OF RECTANGULAR HOLLOW WAVEGUIDES CONNECTED TO EACH OTHER IN A MAGIC TEE CONFIGURATION, EACH OF SAID WAVEGUIDES HAVING AT LEAST ONE SOLID RIDGE FORMED ON A SIDE THEREOF, A PLURALITY OF SAID RIDGES BEING TAPERED FROM A FIRST CROSS-SECTIONAL AREA AT THE FREE END OF THE CORRESPONDING WAVEGUIDE TO A SECOND CROSS-SECTIONAL AREA AT THE POINT OF JUNCTURE TO PROVIDE IMPEDANCE MATCHING THE JUNCTION OVER A WIDE FREQUENCY BAND. 